CYTOCHROMES P450 (CYP) IN TROPICAL FISHES - CATALYTIC ACTIVITIES, EXPRESSION OF MULTIPLE CYP PROTEINS AND HIGH-LEVELS OF MICROSOMAL P450 INLIVER OF FISHES FROM BERMUDA

Hepatic microsomes prepared from 10 fish species from Bermuda were stu died to establish features of cytochrome P450 (CYP) systems in tropica l marine fish. The majority (7/10) of the species had total P450 conte nt between 0.1 and 0.5 nmol/mg, and cytochrome b(5) content between 0. 025 and 0.25 nmol/mg. Ethoxycoumarin O-deethylase (ECOD) and aminopyri ne N-demethylase (APND) rates in these 7 species were 0.23-2.1 nmol/mi n/mg and 0.5-11 nmol/min/mg, respectively, similar to rates in many te mperate fish species. In contrast to those 7 species, sergeant major ( Abudefduf saxatilis) and Bermuda chub (Kyphosus sectatrix) had microso mal P450 contents near 1.7 nmol/mg, among the highest values reported in untreated fish, and had greater rates of ECOD, APND, ethoxyresorufi n O-deethylase (EROD) and pentoxyresorufin O-depentylase than did most of the other species. Freshly caught individuals of all species had d etectable levels of EROD and aryl hydrocarbon hydroxylase (AHH) activi ties. Those individuals with higher rates of EROD activity had greater content of immunodetected CYP1A protein, consistent with Ah-receptor agonists acting to induce CYP1A in many fish in Bermuda waters. Inject ion of tomtate and blue-striped grunt with beta-naphthoflavone (BNF; 5 0 or 100 mg/kg) induced EROD rates by 25 to 55-fold, suggesting that e nvironmental induction in some fish was slight compared with the capac ity to respond. AHH rates were induced only 3-fold in these same fish. The basis for disparity in the degree of EROD and AHH induction is no t known. Rates of APND and testosterone 6 beta- and 16 beta-hydroxylas e were little changed by BNF, indicating that these are not CYP1A acti vities in these fish. Antibodies to phenobarbital-inducible rat CYP2B1 or to scup P450B, a putative CYP2B, detected one or more proteins in several species, suggesting that CYP2B-like proteins are highly expres sed in some tropical fishes. Generally, species with greater amounts o f total P450 had greater amounts of proteins related to CYP2B. These s pecies also had appreciable amounts of CYP3A-like proteins. Thus, many fishes in Bermuda appear to have induced levels of CYP1A; some also h ave unusually high levels of total P450 and of CYP2B-like and CYP?A-li ke proteins. These species may be good models for examining the struct ural, functional and regulatory properties of teleost CYP and the envi ronmental or ecological factors contributing to high levels of express ion of CYP in some fishes. Copyright (C) 1997 Elsevier Science Inc.